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Chapter 27 : Campylobacter jejuni Lipooligosaccharides: Structures and Biosynthesis
Category: Bacterial Pathogenesis
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This chapter reviews the structure, biosynthesis, and genetic determination of Campylobacter jejuni lipooligosaccharides (LOSs), with particular reference to the core oligosaccharide region. In particular, the genetic bases for variation of the outer core are discussed, including gene content variation between LOS loci and mechanisms generating LOS core region variation. Although the chapter predominantly addresses the biosynthesis of the variable LOS outer core of C. jejuni, the biosynthesis and genetic determination of the inner core lipid A region is also examined. Variation in LOS structures is due to diversity of the constituent sugars (number of carbon atoms, ring form, isomeric form, anomeric configuration, etc.), the derivatization of the sugars with noncarbohydrate moieties, and the linkages between the individual sugars (or monosaccharides). The formation of these linkages is determined by the glycosyltransferases and other transferases encoded in the LOS biosynthesis locus. Sugar availability for incorporation into LOS is often determined by enzymes from the LOS biosynthesis locus that are involved in synthesis of sugar intermediates such as cytidine monophosphate-5-N-acetylneuraminic acid (CMPNeu5Ac). There is evidence of recombination occurring within the LOS locus to create mosaics of different classes. Functions can be assigned to 12 of the 13 open reading frames (ORFs) present in the LOS biosynthesis locus of OH4384, the only exception being ORF 12a. The variety of capsular polysaccharide (CPS) structures and biosynthesis loci observed in C. jejuni suggests that it would contribute as much as the LOS repertoire to an open pan-glycome.
C. jejuni LOS outer core structures exhibiting molecular mimicry of gangliosides. Core structures of (A) serostrains HS:19 and HS:4 (GM1a and GD1a mimics), (B) isolate OH4384 (GT1a mimic), (C) isolate OH4382 (GD3 mimic), (D) serostrain HS:10 and isolate PG836 (GD3 and GD1c mimics), (E) serostrain HS:1 (GM2 mimic), (F) serostrain HS:2 (GM3 mimic, i.e., without Gal-β(1,3)-GalNAc-β(1,4)) and NCTC 11168 (also HS:2 serotype but outer core mimics GM1a and GM2 due to phase-variable terminal Gal), (G) serostrains HS:23 and HS:36 (GM2 mimic), and (H) phase-variable strain 81-176 (GM2 and GM3 and mimics predominantly, but also GD1b and GD2). All sugars are in the pyranosidic form and are d-enantiomers. Gal, galactose; GalNAc, N-acetyl-galactosamine; Glc, glucose; Hep, l–glycero–d–manno-heptose; Kdo, 2-keto-3-deoxyoctulosonic acid; Neu5Ac, N-acetylneuraminic acid; P, phosphate; PEtn, phosphoethanolamine.
Campylobacter LOS outer core structures that are not mimicking gangliosides. C. jejuni serostrain HS:3 (A), C. coli serostrain HS:30 (B), C. lari ATCC 35221 (C), and C. lari PC 637 (D). All sugars are in the pyranosidic form and are d-enantiomers. Gal, galactose; GalNAc, N-acetyl-galactosamine; Glc, glucose; GlcNAc, N-acetyl-glucosamine; Hep, l–glycero- d–manno-heptose; Kdo, 2-keto-3-deoxyoctulosonic acid; P, phosphate; PEtn, phosphoethanolamine; Qui3NAc, N-acetylated 3-amino-3,6-dideoxyglucosamine (quinovosamine); Qui3Nacyl, quinovosamine N-acylated with 3-hydroxybutanol or 3-hydroxy-2,3-dimethyl-5-oxoprolyl chains.
C. jejuni LOS classes that possess a sialyltransferase gene. Classes A, B, C, M, and R (C. T. Parker et al., unpublished data).
C. jejuni LOS classes related to LOS class D, class F, and class G (C. T. Parker et al., unpublished data).
C. jejuni LOS classes that possess genes similar to those required for biosynthesis of 6-deoxysugars, rmlA and rmlB homologs (C. T. Parker et al., unpublished data).
Biosynthesis of the LOS core in C. jejuni OH4384. Adapted from Gilbert et al. (2005) .
Alternative extensions of the LOS outer core from HepII.
Biosynthesis of class C core structures.
Biosynthesis of class A core structures with a sialylated inner Gal.
Biosynthesis of classes A and B core structures with a nonsialylated inner Gal.
Biosynthesis of class B core structures extended from Glc-β(1,2)-HepII.
Alternative structures resulting from different combinations of Cst-II and SOAT variants.
Variants of glycosyltransferases and sialate O-acetyltransferase (SOAT) involved in the biosynthesis of LOS outer cores